Genetic transformation requires that the 5′ end of the heterologous transgene is operably connected to a relevant promoter, in order to facilitate expression. Promoters are typically a region of nucleotide sequence located upstream of the 5′ end of coding sequence and provide a binding site for RNA polymerase and any required transcription factors, thereby enabling the initiation of transcription.
Many promoters are constitutive and operate in multiple tissues in the plant. In cases where the object is to express the transgene in a particular tissue, then a tissue specific promoter is required. Seed, and even embryo or endosperm, specific promoters are known and have been used to express genes in seed, grain, and parts thereof (e.g. Abbitt, 2009; Broglie et al., 2002; Furtado et al., 2009; Kridl and Knauf 1995). In the case where genes are primarily or entirely expressed in the roots, a root specific promoter can provide control of gene expression is a desirable manner. Without intending to be limited, examples where root specific expression can provide valuable benefits include manipulating root size and structure; altering geotropism; drought tolerance and water relations; salt tolerance; pH control and buffering with the environment; controlling exudates; signal interactions with the soil microbiome; lowering biotic and abiotic stresses; endogenous hormone control; improving nutrient acquisition; altering root storage capacity; root lodging; disease control; insect control; nematode control; fungal control; microbial control; viral control; phytoremediation. Thus, there are many potentially valuable benefits from having strong specific root promoters.
A requirement arose for a root specific promoter (RSP). Some work has been done to design root specific promoters based on particular elements, but that approach has now been abandoned (Bruce and Niu, 2001). Accordingly, there is a need in the art for novel plant promoter sequences to efficiently drive expression of sequences of interest in tissues-specific basis, and particularly, in a root-specific basis.